Stream Periphyton Development in Relation to Current Velocity and Nutrients

Abstract

Measurement of chlorophyll a accrual on flattened rock substrates placed in streams revealed that a velocity increase up to ~50 cm∙s⁻¹ enhanced periphytic algae accumulation when orthophosphate-phosphorus concentration exceeded 40–50 μg∙L⁻¹. At lower P concentrations velocity increases reduced the accrual rate. The erosive effect of current was hypothesized to retard accumulation unless nutrient availability was such that the positive influence of turbulent diffusion of dissolved substances, and consequent cell growth, overcame frictional shear. Velocity increments above 50 cm∙s⁻¹ eroded an increasingly greater proportion of the periphyton growth. The definition and use of a heterotrophic index as the ratio of adenosine triphosphate to chl a demonstrated that current velocity increases assisted the accumulation of the attached consumers relative to that of the primary producers. Comparison of heterotrophic indices before and after elevated storm runoff currents showed smaller reductions in the standing crop of the periphytic heterotrophs than that of the autotrophs.Key words: periphyton, current velocity, nutrients, phosphorus, chlorophyll a, adenosine triphosphate, heterotrophs